938 
FXUS66 KPQR 172213
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR 
213 PM PST Thu Jan 17 2019

.SYNOPSIS...A vigorous low off the south Washington coast will move
north tonight maintaining showery weather across much of the region,
along with breezy conditions. Heavy rain is expected with the next
frontal system late Friday morning through Friday night with another
round of breezy condition Friday night. This front stalls to our
south on Saturday, but lifts back across the area Sat night. Rainy
weather continues through Sunday. High pressure will slowly dry out
the area Monday and Tuesday. 
&&

.SHORT TERM...Tonight through Sunday Night...A low currently around
300 miles offshore of the Columbia River Bar will continue producing
showers across SW Washington and NW Oregon tonight. Rainfall totals
will will be highest for the Willapa Hills and the SW Washington
Cascades and Foothills where where 0.75 inch of rain is possible
through late tonight. The north Oregon coast, coast range, and
foothills can expect 0.25 to 0.5 inch of rain tonight with less than
0.25 inch for the interior valleys. The snow levels will hover around
4000 feet, and have continued the elevation based Winter Weather
Advisory for the SW WA Cascades. 

East winds are still easing through the Columbia River Gorge, and
the temperatures in the Gorge are beginning to rise above freezing.
Temperatures in the Upper Hood River Valley have been slower to warm,
but elevations below 1300 feet are now above freezing, which provides
greater confidence that the precipitation type will be mostly rain
for much of the Hood River Valley tonight.

South winds are increasing along the coast this afternoon and will be
quite gusty along the beaches and headlands this evening with gusts
of 45-50 mph possible. Wind gusts in the interior valleys will be
around 30kt this evening. 

The offshore buoys are showing rising seas this afternoon as a
powerful swell moves into the waters. The open ocean swell are
running around 4 feet below the ENP forecast, but the swell will
still likely peak in the low 20s late this afternoon and produce
large breakers along the beaches through this evening.

Showers will decrease overnight tonight into Friday morning, but the
next Pacific system will bring additional rain to the coast late
Friday morning that will spread quickly inland in the early
afternoon. The initial rain will be from a very moist warm front that
will lift SW to NE across the area Friday afternoon before a vigorous
cold front moves across the area Friday night. Gusty winds will
accompany the cold front and expect another round of 45-50 mph gusts
for the coast and 30-35mph gusts for the Willamette Valley. 

The cold front moves south early Saturday morning, then stalls over
SW Oregon (south of Lane County) on Saturday. This will provide a
lull in rain on Saturday, but it will not be 'dry' as showers will
linger. The cold front then lifts north back over the area Saturday
night before another low approaches and moves it inland across the
area on Sunday. These fronts will result in a wet weekend with
rainfall amounts of 1.5 to 3.5 inches from Friday afternoon through
Sunday night. The highest rain will be over the Central Oregon coast
range and the Lane County Cascades. Expect rapid rises in area
rivers, but do not expect much river flooding due to the river levels
currently being fairly low.   

The snow levels will rapidly rise with the warm front Friday night
and be around 8500 feet Friday night. The rain may melt the snow pack
some and contribute to some of the rises on the rivers. However, the
snow levels lower on Saturday and will be back to around 4500-5000
feet Saturday night and Sunday. Showers decrease Sunday night as
the responsible low moves inland. ~TJ

.LONG TERM...Monday through Wednesday...Upper troughing continues 
traversing southeast through next week, allowing upper ridging to 
build east over the Pacific to near the US west coast by midweek. 
However, as the ridge axis remains offshore during this period, the 
local area will be in the north to northwesterly flow on its front 
side, still allowing the intrusion of shortwaves. All this to say 
the extended period likely won't be as dry as ridging could imply. 
Models are in agreement with the synoptic pattern through the long 
term period, but there are some discrepancies regarding timing and 
strength of shortwaves and upper lows which introduce uncertainty 
into the forecast. Will likely see some dry periods early next week, 
but with the timing differences between the models, it's difficult 
to pin those exact periods down at this point. Used a blend of 
models for the forecast, trending toward the climatological PoP (40%-
50% currently) during the periods of most significant difference 
between the models. Snow levels look like they'll remain in Cascade 
elevations with no love for low-elevation snow enthusiasts. Bowen
&&

.AVIATION...Overall flight conditions starting to show a
deteriorating trend early this afternoon with increasing MVFR
coverage, especially along the coast. Coastal areas, the Upper
Hood River Valley and Central Gorge north to the south side of
Mt. Adams to remain mainly MVFR through tonight. Increasing VFR
for the coast overnight, then predominant VFR by 12Z Fri. Slower
improvement for the Central Gorge and Upper Hood River Valley.
Inland areas will have a mix of MVFR and VFR through about 06Z
Fri then become primarily VFR. Offshore flow through the Gorge
continues to weaken early this afternoon and becomes neutral by
06Z Fri. Increasing south wind along the central coast and
interior valleys this afternoon, spreading north by early
evening. 

KPDX AND APPROACHES...VFR conditions to be the predominant
category through 18Z Fri. East wind continues through the Gorge,
but will diminish over the next few hours. At 21Z the KTTD-KDLS 
gradient had eased to -4.0 mb. Models suggest the gradient 
becomes neutral this evening. There is the possibility of LLWS 
late this afternoon through the evening with E-SE wind at the 
surface and S-SW wind 30-40 kt near FL020. Also, apparent speed
shear has been noted at KHIO earlier this afternoon with an
urgent pilot report indicating +/- 20 kt. Expect this to remain a
concern through the evening. Weishaar

&&

.MARINE...A 982 mb low center near 48N 129W at 21Z will continue
to weaken and move north through tonight. 18Z ASCAT pass showed
the strongest wind speeds (gales) along the coastline to about 
10 nm and also on the northeast quadrant of the low. 21Z buoy
reports had 35-40 kt gusts. Earlier, 46050 recorded around 45 kt.
Will maintain the current gale warning with an ending time of 06Z
Fri. There will be a short lull in wind overnight through early
Fri morning. 12Z models show another low forming out near 42N
140W 12Z Fri. The associated warm front migrates through the
waters Fri, with the corresponding wind speed increase. 12Z
guidance, especially the NAM, indicates 35 kt wind speeds
returning to PZZ275 as early as 15Z-18Z Fri. The GFS is a little
lighter, closer to 30 kt. By 00Z Sat gales are expected over the
entire area with the NAM and GFS indicating up to 45 kt boundary
layer wind speeds across PZZ275. The NAM also has a few 50 kt
flags at 975 mb over the far outer portion of PZZ275 Fri
afternoon. Will issue another gale warning valid 18Z Fri through
14Z Sat with this package and cap gusts at 45 kt. Wind speeds
fall to around 15-20 kt Sat afternoon. 

Increasing model disparity begins Sat night regarding another
surface low. The 18Z NAM is much different than its 12Z version.
Models agree the Sun/Sun night low weakens and heads toward the
South Oregon waters. Would tend to favor that track based on
history of previous lows. Likely to end up with small craft
advisory level wind Sun over the central zones. 

21Z buoy reports indicated 23-foot seas at buoy 46089, 20 feet at
46050 and 18 feet for 46029. 12Z ENP guidance at buoy 46089 valid
18Z appeared to be at least 4-5 ft too high. Buoy 46002 may have
peaked at 27 ft at 20Z. The ENP model indicated 32 ft at 12Z,
which was several feet too high. In any event, 20-25 ft still
looks plausible through tonight. Seas ease below 20 ft by early
Fri morning, but will ramp up to near or slightly above 20 ft
again late Fri night or early Sat morning with the next round of
gales. Wave heights lower to below 15 ft Sat night and to 10 ft
by Sun afternoon. Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...High Surf Advisory until 10 AM PST Friday for North Oregon 
     Coast.

     High Surf Warning until 10 AM PST Friday for Central Oregon 
     Coast.

WA...High Surf Advisory until 10 AM PST Friday for South Washington 
     Coast.

     Winter Weather Advisory until 4 AM PST Friday for South 
     Washington Cascades.

PZ...Gale Warning until 10 PM PST this evening for Coastal Waters 
     from Cape Shoalwater WA to Florence OR out 60 NM.

     Gale Warning from 10 AM Friday to 6 AM PST Saturday for Coastal 
     Waters from Cape Shoalwater WA to Florence OR out 60 NM.

     Small Craft Advisory for Rough Columbia River Bar until 4 PM 
     PST Friday.

&&
$$

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This discussion is for Northwest Oregon and Southwest Washington 
from the Cascade crest to 60 nautical miles offshore. This area is 
commonly referred to as the forecast area.